In the cone crushers of the type defined above, when the material to be crushed is fed into the crushing cavity, this material is simultaneously frictioned against the head and the upper housing, causing the cone head to rotate in a direction opposite to the rotation direction of the eccentric element. The material being supplied prevents the cone head from being rotatively dragged by the eccentric element, maintaining said cone head rotatively stationary relative to the upper housing.
Thus, in the “on-load” operation, the cone head is prevented from rotating with the eccentric element, by the braking action provided by the material being crushed. The braking force exerted by the material is greater than the friction force applied on the opposite direction, between the cone head and the rotating eccentric element.
However, during the “no-load” operation of the crusher, that is, when no material is being crushed in the crushing cavity, and the eccentric element continues to rotate around the vertical axle, there is no material in the crushing cavity to exert a frictional braking force between the cone head and the upper housing mounted to the structure of the crusher.
In the “no-load” operation, the friction between the cone head and the eccentric element is sufficient to make the cone head be rotatively dragged by the eccentric element, tending to reach the same operational rotation of the latter.
Nevertheless, in said “no-load” operating condition, when the material to be crushed is fed into the crushing cavity, it makes frictional contact simultaneously with the stationary crushing surface of the upper housing and with the rotating crushing surface of the cone head, provoking an abrupt braking of the latter against the great inertia force of its rotating mass. This operational condition is highly inconvenient, since it causes an intense wear of the crushing surfaces, usually defined by hard-material coatings applied to the cone head and to the upper housing.
Another negative aspect of the cone head rotating jointly with the eccentric element is the tendency of the crusher to violently throw, outwardly from the crushing cavity, the first particles of stone, ore, coal and others introduced into the crusher operating in the “no-load” mode, under the risk of causing injury to the operators and damages to the machine.
A known solution for preventing the cone head from rotating together with the eccentric element provides a sort of one-way locking clutch in the interior of the crusher, in order to prevent the cone head from being rotatively dragged by the eccentric element in the “no-load” operation of the crusher, but allowing the cone head to rotate in the direction opposite that of the upper housing, in the “on-load” operation of the crusher. However, this solution presents, as drawbacks, the high cost of the clutch and of its assembly, as well as maintenance difficulties. Furthermore, in the “on-load” operational condition, the cone head is frequently forced to rotate in the locking direction of the clutch, damaging the latter.